1. Field of the Invention
The present invention relates to an image processing apparatus which has a portion of luminance levels at which tones cannot be expressed on a display unit due to a latitude difference between a recording image and display image, and a control method thereof.
2. Description of the Related Art
Digital camera parameters include “latitude” as one important item. “Latitude” is a reproducible exposure range or tolerance level of an object, and is determined by settings of an exposure value using an aperture diaphragm and a gamma characteristic as in a dynamic range. A characteristic which can reproduce an image even by setting an exposure value that normally causes highlight-detail loss or shadow-detail loss is expressed as “wide latitude”. In case of such characteristic, smooth tones can be reproduced from a dark part to a bright part. Conversely, a characteristic with a narrow reproducible exposure range is expressed as “narrow latitude”. In this case, highlight-detail loss or shadow-detail loss is readily caused for overexposure or underexposure, but a high-contrast image can be obtained.
A wide variety of digital video cameras ranging from home use to professional use (for film/commercial production) are available, and concepts about latitudes of images to be recorded are different for respective users.
In home use of a digital video camera, an image is converted into and saved as latitude-restricted image data based on an exposure value using an aperture diaphragm and gamma characteristics at the time of developing processing in correspondence with a performance of a display unit such as a television monitor upon recording an image. By contrast, in professional use for filming, an image is recorded to have a wide latitude while utilizing a sensor performance of a digital video camera as much as possible, and the latitude is restricted in correspondence with the performance of the display unit at the time of editing.
FIG. 3 shows the configuration of a conventional home-use digital video camera in which latitudes of a recording image and display images are matched. In FIG. 3, image data captured by an image sensor 102 is converted by a developing processing unit 104 based on a desired developing gamma characteristic, and is recorded in a recording medium 107. On the other hand, image data to be displayed on a display unit 111 is obtained by converting output image data of the developing processing unit 104 by a gamma correction unit 108 based on display gamma characteristics which can attain a linear characteristic between object and display luminance values in correspondence with the characteristic of the display unit 111. The user adjusts an exposure value by an aperture diaphragm 101 based on an image, zebra pattern, or the like displayed on the display unit 111. The zebra pattern is an assist display required to notify the user that an output of a corresponding region of the image sensor is saturated by additionally displaying an oblique stripe pattern to that region corresponding to a predetermined luminance level to the image displayed on the display unit 111. Since other units will be described later as an embodiment (FIG. 1), a description thereof will not be given.
Japanese Patent Laid-Open No. 04-051381 describes a technique which extracts a maximum-level signal from R, G, and B image signal of an image sensor, and displays a zebra pattern on a display image within a saturation range of one of the R, G, and B image signals when any of the R, G, and B image signals exceeds a saturation detection level.
As described above, in professional use for filming, since a wide latitude of a recording image is assured, but a latitude of a display image is restricted to a gamma characteristic corresponding to the characteristic of a display unit, the recording image and display image have different latitudes. For this reason, an image signal of a latitude not less than that restricted by the display gamma characteristic causes a highlight-detail loss, and accurate exposure adjustment is difficult to attain upon confirmation of a captured image. Hence, it is desirable to make an assist display which allows the user to confirm a latitude difference between a recording image and display image.